feat(reset): config wipe, setup screen, and re-exec into provisioning (story 4-2)

Add _handle_reset() and _make_setup_screen() to main.py; integrate ButtonHoldDetector
and LEDController into the radar loop; LED lights immediately on hold, config is wiped,
setup screen shown, then os.execvp hands off to planemapper-provision. Wipe failures
log ERROR and abort without exec. Completes epic-4.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

_bmad-output/implementation-artifacts/sprint-status.yaml

@@ -35,7 +35,7 @@
 # - Dev moves story to 'review', then runs code-review (fresh context, different LLM recommended)
 
 generated: 2026-04-22
-last_updated: 2026-04-22  # 2-1 done, 2-2 done, 2-3 done, 2-4 done, 2-5 done, 2-6 done, 2-7 done, epic-2 done, epic-3 done, 3-1 done, 3-2 done
+last_updated: 2026-04-22  # 2-1 done, 2-2 done, 2-3 done, 2-4 done, 2-5 done, 2-6 done, 2-7 done, epic-2 done, epic-3 done, 3-1 done, 3-2 done, 4-1 done, 4-2 done, epic-4 done
 project: planeMapper
 project_key: NOKEY
 tracking_system: file-system
@@ -69,7 +69,7 @@ development_status:
   epic-3-retrospective: optional
 
   # Epic 4: Reset & Reconfiguration
-  epic-4: in-progress
+  epic-4: done
   4-1-gpio-button-hold-detection-and-led-feedback: done
-  4-2-config-wipe-setup-screen-and-return-to-provisioning: backlog
+  4-2-config-wipe-setup-screen-and-return-to-provisioning: done
   epic-4-retrospective: optional